Development of Novel Decarboxylation-Urea Method toward Interlayer-Anion-Controlled Layered Double Hydroxides
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ABSTRACT:
SUBMITTER: Uga M
PROVIDER: S-EPMC10552090 | biostudies-literature | 2023 Sep
REPOSITORIES: biostudies-literature
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Project description:Research on two-dimensional materials is one of the most relevant fields in materials science. Layered double hydroxides (LDHs), a versatile class of anionic clays, exhibit great potential in photocatalysis, energy storage and conversion, and environmental applications. However, its implementation in real-life devices requires the development of efficient and reproducible large-scale synthesis processes. Unfortunately, reliable methods that allow for the production of large quantities of two-dimensional LDHs with well-defined morphologies and high crystallinity are very scarce. In this work, we carry out a scale-up of the urea-based CoAl-LDH synthesis method. We thoroughly study the effects of the mass scale-up (25-fold: up to 375 mM) and the volumetric scale-up (20-fold: up to 2 L). For this, we use a combination of several structural (XRD, TGA, and N2 and CO2 isotherms), microscopic (SEM, TEM, and AFM), magnetic (SQUID), and spectroscopic techniques (ATR-FTIR, UV-vis, XPS, ICP-MS, and XANES-EXAFS). In the case of the volumetric scale-up, a reduction of 45% in the lateral dimensions of the crystals (from 3.7 to 2.0 µm) is observed as the reaction volume increases. This fact is related to modified heating processes affecting the alkalinization rates and, concomitantly, the precipitation, even under recrystallization at high temperatures. In contrast, for the tenfold mass scale-up, similar morphological features were observed and assigned to changes in nucleation and growth. However, at higher concentrations, simonkolleite-like Co-based layered hydroxide impurities are formed, indicating a phase competition during the precipitation related to the thermodynamic stability of the growing phases. Overall, this work demonstrates that it is possible to upscale the synthesis of high-quality hexagonal CoAl-LDH in a reproducible manner. It highlights the most critical synthesis aspects that must be controlled and provides various fingerprints to trace the quality of these materials. These results will contribute to bringing the use of these 2D layered materials closer to reality in different applications of interest.
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Project description:Despite their diverse application profile, aromatic organochlorides such as 2,4,6-trichlorophenol (TP) are widely renowned for creating a negative toll on the balance of the ecosystem. Strict regulatory regimes are required to limit exposure to such organic pollutants. By deployment of a straightforward detection scheme, electrochemical sensing technology offers a competitive edge over the other techniques and practices available for pollutant monitoring. Here, we present a streamlined hydrothermal approach for synthesizing copper-manganese layered double hydroxide (CuMn-LDH) rods to be employed as electrocatalysts for detecting TP in various media. With a focused intention to leverage the full potential of the prepared CuMn-LDHs, the interlamellar region is configured using a series of intercalants. Further, a thorough comparative analysis of their structures, morphologies, and electrochemical performance is accomplished using various analytical techniques. The electrocatalytic oxidation ability of the CuMn-LDH toward TP molecules is markedly altered by incorporating various anions into the gallery region. The dynamic attributes of the developed sensor, such as a wide linear response (0.02-289.2 μM), a low detection limit (0.0026 μM), and good anti-interfering ability, acclaim its superior viability for real-time detection of TP with exceptional tolerance to the presence of foreign moieties. Hence, this work manifests that the nature of intercalants is a vital aspect to consider while designing LDH-based electrochemical probes to detect priority pollutants.
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Project description:The urge for carbon-neutral green energy conversion and storage technologies has invoked the resurgence of interest in applying brucite-type materials as low-cost oxygen evolution reaction (OER) electrocatalysts in basic media. Transition metal layered hydroxides belonging to the brucite-type structure family have been shown to display remarkable electrochemical activity. Recent studies on the earth-abundant Fe3+ containing mössbauerite and Fe3+ rich Co-Fe layered oxyhydroxide carbonates have suggested that grafted interlayer anions might play a key role in OER catalysis. To probe the effect of such interlayer anion grafting in brucite-like layered hydroxides, we report here a systematic study on the electrocatalytic performance of three distinct Ni and Co brucite-type layered structures, namely, (i) brucite-type M(OH)2 without any interlayer anions, (ii) LDHs with free interlayer anions, and (iii) hydroxynitrate salts with grafted interlayer anions. The electrochemical results indeed show that grafting has an evident impact on the electronic structure and the observed OER activity. Ni- and Co-hydroxynitrate salts with grafted anions display notably earlier formations of the electrocatalytically active species. Particularly Co-hydroxynitrate salts exhibit lower overpotentials at 10 mA cm-2 (η=0.34 V) and medium current densities of 100 mA cm-2 (η=0.40 V) compared to the corresponding brucite-type hydroxides and LDH materials.
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Project description:Water-containing layered materials have found various applications such as water purification and energy storage. The highly structured water molecules around ions under the confinement between the layers determine the ion storage ability. Yet, the relationship between the configuration of interlayer ions and water structure in high ion storage layered materials is elusive. Herein, using layered double hydroxides, we demonstrate that the water structure is sensitive to the filling density of ions in the interlayer space and governs the ion storage. For ion storage of dilute nitrate ions, a 24% decrease in the filling density increases the nitrate storage capacity by 300%. Quartz crystal microbalance with dissipation monitoring studies, combined with multimodal ex situ experiments and theoretical calculations, reveal that the decreasing filling density effectively facilitates the 2D hydrogen-bond networking structure in water around interlayer nitrate ions along with minimal change in the layered structure, leading to the high storage capacity.
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Project description:A novel nanocomposite bead LaLiAl-LDH@201 was fabricated by doping a small amount of La into nanocrystalline Li/Al layered double hydroxides (LDHs) pre-confined inside polystyrene anion exchanger D201 (LiAl-LDH@201). A systematic characterisation of the resultant LaLiAl-LDH@201 (XRD, SEM-EDS, TEM-EDS, and XPS) evidenced the successful incorporation of La into the Li/Al LDHs, with their interlayer distance expanded to allow more exchangeable sites for fluoride uptake. The resultant LaLiAl-LDH@201 showed high and stable defluoridation performance over a wide range of pH from 4 to 9. The superior uptake capacity and affinity for fluoride of LaLiAl-LDH@201 over LiAl-LDH@201 were driven by both the increased anion exchange capacity of the embedded LDHs and the specific La-F interaction evidenced via XPS and TEM-EDS characterisation. Fixed-bed column test confirmed that the working capacity of LaLiAl-LDH@201 for defluoridation of authentic fluoride-rich groundwater was nearly twice that of LiAl-LDH@201. The fluoride-loaded LaLiAl-LDH@201 could be conveniently regenerated in situ by using NaOH + NaCl binary solution, achieving desorption efficiency above 98%. Moreover, negligible capacity loss, La leaching, or structure alteration was observed after five adsorption-regeneration cycles, indicating the high stability of LaLiAl-LDH@201. Therefore, the novel millisphere nanocomposite LaLiAl-LDH@201 was promising for efficient defluoridation from water and wastewater.
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Project description:Layered double hydroxides (LDHs) constitute a unique group of 2D materials that can deliver exceptional catalytic, optical, and electronic performance. However, they usually suffer from low stability compared to their oxide counterparts. Using density functional calculations, we quantitatively demonstrate the crucial impact of the intercalants (i.e., water, lactate, and carbonate) on the stability of a series of common LDHs based on Mn, Fe, and Co. We found that intercalation with the singly charged lactate results in higher stability in all these LDH compounds, compared to neutral water and doubly charged carbonate. Furthermore, we show that the dispersion effect aids the stability of these LDH compounds. This investigation reveals that certain intercalants enhance LDH stability and alter the bandgap favourably.
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Project description:We report a general method for the synthesis of core-shell hybrid materials containing a microporous zeolite core with an aqueous miscible organic-layered double hydroxide (AMO-LDH) shell using a simple in situ coprecipitation method. For example, zeolite-HY@AMO-Mg2Al-CO3-LDH contains a 150 nm hierarchical AMO-Mg2Al-CO3-LDH surface coating on zeolite-HY. It exhibits a similar BET surface area (698 m2 g-1) as the parent zeolite-HY but this surface area has been re-allocated between microspores and mesopores. We believe that surface aluminium sites act as nucleation sites for the formation of the LDH coating and so robustly links it into the zeolite lattice. We expect that this new hybrid structure with micropores dominating in the core and mesopores populating the shell will provide a desirable new hybrid structure type for adsorption or catalysis.
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Project description:Guanosine monophosphates (GMPs) were intercalated into the interlayer space of layered double hydroxides (LDHs) and the molecular arrangement of GMP was controlled in LDHs. The intercalation conditions such as GMP/LDH molar ratio and reaction temperature were systematically adjusted. When the GMP/LDH molar ratio was 1:2, which corresponds to the charge balance between positive LDH sheets and GMP anions, GMP molecules were well-intercalated to LDH. At high temperature (100 and 80 °C), a single GMP molecule existed separately in the LDH interlayer. On the other hand, at lower temperature (20, 40 and 60 °C), GMPs tended to form ribbon-type supramolecular assemblies. Differential scanning calorimetry showed that the ribbon-type GMP assembly had an intermolecular interaction energy of ≈101 kJ/mol, which corresponds to a double hydrogen bond between guanosine molecules. Once stabilized, the interlayer GMP orientations, single molecular and ribbon phase, were successfully converted to the other phase by adjusting the external environment by stoichiometry or temperature control.
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Project description:Novel modified Ni/Fe layered double hydroxides with different morphology of spherical - like shape were fabricated via using urea as a ligand and glycerol (Ni/Fe LDH/GL) with Ni:Fe molar ratios of 2:1 by the simplest co -precipitation method. Also, for comparison purposes, Ni/Fe LDH was synthesized to be used as a control one. A suggested interpretation for the morphology change was also given. The materials were characterized by X-ray diffraction (XRD), The Fourier transform infrared (FT - IR) spectroscopy, field emission scanning electron microscopy (FESEM), EDX for elemental analysis, high resolution transmission electron microscopy (HRTEM), Brunauer, Emmett, and Teller (BET) equation, particle size distributions and Zeta potential measurements. In addition, the synthesized materials were used as adsorbents for removal of potassium dichromate from aqueous solutions under various experimental conditions. The adsorption of Cr (VI) was strongly pH dependant and the pHPZC was studied. Kinetic studies were evaluated through different models including, pseudo first and second orders, mixed 1, 2 orders, intra particle diffusion and Avrami models. For adsorption isotherms, two-parameter models (Langmuir, Freundlich and Temkin) and three parameter models (Sips, Langmuir-Freundlich and Tooth) were investigated showing maximum adsorption capacity of 50.43 mg/g and 136.05 mg/g for Ni/Fe LDH and Ni/Fe LDH/GL, respectively. Also, the effect of temperature was investigated at (23, 35, 45, 55 °C) and the thermodynamic parameters (∆H°, ∆S° and ∆G°) were calculated showing exothermic and spontaneous adsorption process. The effect of coexisting anions (Cl-, SO42- and HPO42-) and humic acid at different concentrations on the removal efficiency of dichromate ions was investigated. Chemical stability and recyclability of these adsorbents were also studied. The intermolecular hydrogen bonds formation between dichromate ion, urea, glycerol, LDH was explored by Monte Carlo simulation This study suggested that the modified Ni/Fe LDH/GL materials were promising nanoadsorbents for efficient potassium dichromate removal.
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Project description:This paper details a successful synthesis and comparison of a range of tri-metal hydrotalcite-like layered double hydroxides (LDHs) using urea hydrolysis. Transition-metal-substituted MgMAl-LDHs were synthesized with M = Fe, Co, Ni, Cu or Zn. 5 mol% and 10 mol% substitutions were performed, where Mg was substituted with Co, Ni, Cu and Zn, and Al with Fe. The successful synthesis of crystalline MgMAl-LDHs was confirmed using X-ray powder diffraction (XRD) analysis. Energy-dispersive X-ray (EDX) spectroscopy was used to identify substituted metals and determine changes in composition. Changes in morphology were studied using scanning electron microscopy (SEM). Thermogravimetric analysis was used to determine the effect of Fe-, Co-, Ni-, Cu- or Zn-substitution on the thermal degradation of the MgMAl-LDH phase. The structure, morphology and thermal behavior of the LDHs were shown to be influenced by the substituted transition metals. The observed thermal stability took the order MgNiAl- > MgFeAl- = MgAl- ≥ MgCoAl- > MgCuAl- > MgZnAl-LDH. The urea hydrolysis method was shown to be a simple preparation method for well-defined crystallite structures with large hexagonal platelets and good distribution of transition metal atoms in the substituted LDHs.
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